A1 preamplifier, de-esser

//A1 preamplifier, de-esser
A1 preamplifier, de-esser 2017-04-22T06:46:15+00:00

The A1 is our first analog input/output only product. A state-of-the-art microphone/line pre-amplifier with a de-esser in the popular API 500 Series format. The side-chain of the de-esser uses a DSP – unique but advantageous for the precision of the side-chain and enabling the use of a very low noise gain element. Two modules can be side-chain linked for stereo operation.

It has a transformer balanced wide level range input with a pad for line level sensitivity. The input gain is set with a sixteen position switch. A low cut filter is useful for microphone work. Phantom power can be switched on or off.

The output is also transformer balanced and has an additional potentiometer to set the output level independently from the levels the de-esser is running at. A polar its switch allows to change the absolute polarity of the output signal.

The de-esser section uses a bandpass filter to split the audio band. The bandpass filter parameters are the center frequency and the Q. The Threshold parameter defines the sensitivity of the de-esser side-chain. A few attack and release times and ratios can be selected via DIP switches at the bottom of the unit. A LED indicates whether there is any gain-reduction happening and a “listen” switch allows to listen to the signal filtered by the band-pass. Useful to zoom in on e.g. specific sibilances. The de-esser can be bypassed with a switch. Several LEDs allow to monitor the input and output levels.

Input, pre-amplifier
The A1 microphone pre-amplifier stage uses a transformer-balanced, discrete, class A design with a current-feedback amplifier architecture for low distortion and wide bandwidth across the full gain range. The pre-amplifier sports very low noise for a wide range of source impedances, across the full gain range. The gain is variable in 3 dB steps between 15 and 60 dB. A 24 dB pads allows to feed line levels as well. A high pass filter can be switched in. The corner frequency can be selected to be 40 or 80 Hz.

The de-esser section uses an advanced mixed signal design: The direct signal path is fully analog while the side-chain works in the digital domain. This enables the use of a low distortion precision MDAC (Multiplying D/A Converter) as the variable gain element. The side-chain is built for very low latency, using a 500 kHz sampling frequency.

Front panel controls
The front panel controls for the de-esser section are knobs for frequency, bandwidth and threshold. Further parameters (ratio, attack and release time) can be set via DIP switches.

The output also uses a transformer balanced design with a high maximum output level of +27 dBu. An additional output gain potentiometer allows to set the output level in a wide range.

Compatible with API Series 500 power racks
Current consumption ±16 V supply: ≤ 150 mA
Current consumption +48 V supply: ≤ 15 mA

Depth: 15 cm
Width: 3,8 cm (1 slot)
Height: 13,3 cm

Input gain range, pad off: +15 dB to +60 dB, 3 dB steps
Pad attenuation: 24 dB
Maximum input level at minimum input gain, pad on: +29.7 dBu (for THD+N ≤ −80 dB)
Input impedance at 1 kHz, pad off: 8.4 kΩ
Input impedance at 1 kHz, pad on: 2.8 kΩ

Output gain range: −∞ dB to +12 dB, continuous
Maximum output level, 100 kΩ load: +27.0 dBu (for THD+N ≤ −80 dB)
Output impedance at 1 kHz: 290 Ω